Direct mounting techniques such as flip-chip mounting (FC), direct chip attach (DCA), direct die attach (DDA), and flip chip on board (FCOB) generally involve the fixing of an integrated circuit (IC) die to a printed wiring board (PWB) substrate. The IC die is then encapsulated on the PWB substrate with a molding compound.
As advanced wafer node technologies dictate IC die with higher I/O count, larger body size, and smaller bump pitch, IC die packaging is facing more challenges for warpage concern, particularly under high temperature exposure during solder bump reflow. A common failure mode is known as controlled collapse chip connection (C4) bump short/open (cold joint) or solder ball cold joint on a ball grid array (BGA) ball. As BGA pitch continues to be reduced, package warpage causes cold joints, which affect interconnection reliability and assembly yield. Additionally, cold joints are often not detected during final package testing, since a test normally applies a force on the test probe to maintain physical contact with the IC die. This force can press the package down which makes the solder joint operable during testing, but the joint fails in normal operating conditions.